Synthetic and natural polymers are attacked by oxygen and eventually may become useless for their intended purpose. The chemical reaction by means of which oxygen attacks and degrades many such materials is a free radical chain reaction. Free radicals are produced by abstraction of hydrogen atoms from the molecules of the material by light, heat, mechanical action, active molecules and the like.
The free radicals are extremely reactive in the presence of air and oxygen, forming peroxide radicals, which in turn abstract hydrogen atoms from the molecules to form additional radicals. These again react with oxygen in the same manner. Thus, once started, the reaction is a self-perpetuating degradative continuous chain reaction until stopped. In order to prevent such degradation, various antioxidants have been added which in most instances react with and destroy the intermediate chemical-free radicals as they form, without producing equally reactive intermediates.
Work is continually being done to obtain compounds with improved antioxidative properties particularly for natural and synthetic rubbers, since a number of the more highly commercial uses of natural and synthetic rubbers involve subjecting the rubber to conditions which promote oxidation. Antioxidants for rubbers are generally classified as staining antioxidants if they stain or discolor the rubber or as non-staining antioxidants if they do not substantially change the color the rubber. It has been noted that generally those antioxidants which are of the staining type provide better protection that those which do not stain. Therefore, depending upon the use of the composition, either the amount of protection against oxidation or the color of the material has been compromised. Accordingly, it is an object of the present invention to provide an antioxidant which is non-staining and which also provides as good as if not better protection against oxidation than the commercially available staining types of antioxidants. A further object of the present invention is to provide antioxidants which are relatively inexpensive to produce and which are effective in a myriad of compositions.